accel/tcg: Always lock pages before translation

We had done this for user-mode by invoking page_protect
within the translator loop.  Extend this to handle system
mode as well.  Move page locking out of tb_link_page.

Reported-by: Liren Wei <lrwei@bupt.edu.cn>
Reported-by: Richard W.M. Jones <rjones@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Richard W.M. Jones <rjones@redhat.com>

accel/tcg/cpu-exec.c

@@ -536,6 +536,26 @@ static void cpu_exec_longjmp_cleanup(CPUState *cpu)
     if (have_mmap_lock()) {
         mmap_unlock();
     }
+#else
+    /*
+     * For softmmu, a tlb_fill fault during translation will land here,
+     * and we need to release any page locks held.  In system mode we
+     * have one tcg_ctx per thread, so we know it was this cpu doing
+     * the translation.
+     *
+     * Alternative 1: Install a cleanup to be called via an exception
+     * handling safe longjmp.  It seems plausible that all our hosts
+     * support such a thing.  We'd have to properly register unwind info
+     * for the JIT for EH, rather that just for GDB.
+     *
+     * Alternative 2: Set and restore cpu->jmp_env in tb_gen_code to
+     * capture the cpu_loop_exit longjmp, perform the cleanup, and
+     * jump again to arrive here.
+     */
+    if (tcg_ctx->gen_tb) {
+        tb_unlock_pages(tcg_ctx->gen_tb);
+        tcg_ctx->gen_tb = NULL;
+    }
 #endif
     if (qemu_mutex_iothread_locked()) {
         qemu_mutex_unlock_iothread();

accel/tcg/internal.h

@@ -10,6 +10,7 @@
 #define ACCEL_TCG_INTERNAL_H
 
 #include "exec/exec-all.h"
+#include "exec/translate-all.h"
 
 /*
  * Access to the various translations structures need to be serialised
@@ -35,6 +36,32 @@ static inline void page_table_config_init(void) { }
 void page_table_config_init(void);
 #endif
 
+#ifdef CONFIG_USER_ONLY
+/*
+ * For user-only, page_protect sets the page read-only.
+ * Since most execution is already on read-only pages, and we'd need to
+ * account for other TBs on the same page, defer undoing any page protection
+ * until we receive the write fault.
+ */
+static inline void tb_lock_page0(tb_page_addr_t p0)
+{
+    page_protect(p0);
+}
+
+static inline void tb_lock_page1(tb_page_addr_t p0, tb_page_addr_t p1)
+{
+    page_protect(p1);
+}
+
+static inline void tb_unlock_page1(tb_page_addr_t p0, tb_page_addr_t p1) { }
+static inline void tb_unlock_pages(TranslationBlock *tb) { }
+#else
+void tb_lock_page0(tb_page_addr_t);
+void tb_lock_page1(tb_page_addr_t, tb_page_addr_t);
+void tb_unlock_page1(tb_page_addr_t, tb_page_addr_t);
+void tb_unlock_pages(TranslationBlock *);
+#endif
+
 #ifdef CONFIG_SOFTMMU
 void tb_invalidate_phys_range_fast(ram_addr_t ram_addr,
                                    unsigned size,
@@ -48,8 +75,7 @@ TranslationBlock *tb_gen_code(CPUState *cpu, vaddr pc,
 void page_init(void);
 void tb_htable_init(void);
 void tb_reset_jump(TranslationBlock *tb, int n);
-TranslationBlock *tb_link_page(TranslationBlock *tb, tb_page_addr_t phys_pc,
-                               tb_page_addr_t phys_page2);
+TranslationBlock *tb_link_page(TranslationBlock *tb);
 bool tb_invalidate_phys_page_unwind(tb_page_addr_t addr, uintptr_t pc);
 void cpu_restore_state_from_tb(CPUState *cpu, TranslationBlock *tb,
                                uintptr_t host_pc);